Touch screen systems are available that use two or more camera assemblies that are located in different corners of the touch screen. Each of the camera assemblies includes one linear light sensor and simple optics such as a lens that detects light within a single field of view. One or more infrared light sources may be mounted in proximity to the lens or proximate other areas of the touch screen.
A touch screen system that uses one such camera assembly mounted in one corner of the touch screen and a second such camera assembly mounted in an adjacent corner of the touch screen provides reliable detection of a single touch on the touch screen using triangulation. The detection of the finger or stylus on the touch screen is made by detecting infrared light reflected by the stylus or finger, or by detecting a shadow of the stylus or finger due to the relative lack of light reflected from the bezel of the touch screen. However, some blind spots may occur near each of the camera assemblies where a location of a touch may not be determined.
Touch screen systems capable of detecting two or more simultaneous touches are desirable to increase the functionality for the user. At least one touch screen system therefore includes cameras located in other corners of the touch screen to sense the multiple touches. However, utilizing multiple cameras may increase the overall cost of the touch screen system. It is therefore desirable to provide a less costly device that may sense multiple touches on a touch screen.